In the context of the present invention, the term “headlight” shall be understood to mean not only an entire vehicle headlight, but also an illumination unit, which together with other illumination units, for example, can form part of a headlight.
The development of current headlight systems always focuses on the desire of being able to project a light image onto the roadway that has the highest possible resolution, changes rapidly and can be adapted to the particular traffic, road and lighting conditions. The term “roadway” is used for simplified illustration here since, of course, it depends on the local circumstances whether a light image is in fact located on the roadway or also extends beyond. In principle, the light image, in the meaning in which it is used herein, corresponds to a projection onto a vertical surface in accordance with the relevant standards that refer to motor vehicle lighting technology.
In keeping with the aforementioned need, different headlight systems have been developed, such as, in particular, headlights operating with scanning, modulated laser beams, wherein the lighting-related starting point is at least one laser light source that emits a laser beam and is associated with a laser control unit, which is used for power supply purposes and for monitoring the laser emission or, for example, for controlling the temperature, and which is also configured to modulate the intensity of the emitted laser beam. “Modulating” shall be understood to mean that the intensity of the laser light source can be altered, either continuously or in a pulsed manner, within the meaning of switching on and off. What is essential is that the light output can analogously be dynamically altered, depending on the angular position of a mirror deflecting the laser beam. Additionally, there is also the option of switching on and off for a certain period of time so as not to illuminate or to suppress defined areas. The laser light sources and the micromirror used for beam deflection are controlled via a processing unit, also referred to as ECU (electronic or engine control unit) for short. One example of a dynamic control concept for generating an image by way of a scanning laser beam is described, for example, in document AT 514633 by the applicant.
Since such headlight system can, at times, be very complex and expensive, creating the desire for economical headlights that nonetheless exhibit high flexibility with respect to the generated light image, headlights have become known which utilize image generators as light processing elements, which comprise a large number of controllable pixel fields. DE 10 2013 215 374 A1, for example, shows approaches in which the light of a light source is directed by way of a light conducting element to an LCD image generator, and to an LCoS chip or to a micromirror array (“DMD”), so as to then be projected onto the roadway by way of a projection optics system.
Document DE 11 2013 003 050 T5 discloses a vehicle lamp in which the light of two LEDs is directed by way of a respective reflector onto a DMD, from where it is projected onto the roadway by way of a projection lens. It is possible to generate different illumination patterns on the DMD, which are reproduced on the roadway by the projection lens.
The document FR 3 008 477 A1 also shows a vehicle lamp comprising a projection lens and two light sources, the light of which is directed by way of two different mirror elements to the projection lens, and from there into the traffic space, so as to generate two light fields. This as well as the aforementioned lamp system uses customary lenses as the projection optics system, in which no distinction in terms of regions having different refractive power is possible.
DMD is an acronym denoting “digital micromirror device”, and thus represents a micromirror array or a micromirror matrix. Such a micromirror array has very small dimensions, which are typically in the order of magnitude of 10 mm. In a DMD, micromirror actuators are arranged in a matrix-like manner, wherein each individual mirror element, which has an edge length of approximately 16 μm, for example, can be tilted by a certain angle, for example 20°, for example by electromagnetic or piezoelectric actuators. The end positions of a micromirror are referred to as the ON state and OFF state, wherein ON state shall be understood to mean that light from the micromirror reaches the road via the projection optics system, while it is directed onto an absorber, for example, in the OFF State. Typically, it will also be necessary to ensure absorption of those rays of light that originate from micromirrors when these are not in the “active” angular position thereof and that are not projected by way of the projection optics system onto the road. For this purpose, absorbers or absorber surfaces are used, which absorb what are otherwise harmful rays of light and convert them into heat.
The angle of each micromirror can be adjusted individually, wherein it is possible to switch between the end positions up to 5000 times per second. The number of mirrors corresponds to the resolution of the projected image, wherein a mirror can represent one or more pixels. DMD chips having high resolutions in the megapixel range are available today. The technology underlying the adjustable individual mirrors is the microelectromechanical systems (MEMS) technology.
While the DMD technology has two stable mirror states, and the reflections can be set by way of modulation between the two stable states, the “analog micromirror device” (AMD) technology allows the individual mirrors to be set in variable mirror positions.
A micromirror array-based headlight is described, for example, in DE 195 30 008 A1.
When it comes to headlights of motor vehicles, there is often the desire to implement multiple light functions in as compact a design as possible, such as in particular high beam, low beam, daytime running light and cornering light. Proceeding from a micromirror concept, in this case multiple micromirror arrays and multiple lenses are required for the projection optics system, which results in high material and manufacturing costs.
The configuration of a luminance pattern is implemented not only by way of the modulation of the primary light source, but also by way of different array control units for different light distributions, such as high beam, low beam with or without asymmetry, suppression scenarios and the like, wherein different array control units control the individual micromirror elements as a function of the desired light distribution.
It is an object of the invention to create a headlight that can be produced cost-effectively, but nonetheless offers large design freedom with respect to the light images that can be generated.